The standardization of LTE-A (Long Term Evolution-Advanced) is currently under discussion in 3GPP (3rd Generation Partnership Project) as a next generation communication standard for LTE (Long Term Evolution). A carrier aggregation (CA) technology is introduced in an LTE-A system to maintain backward compatibility with an LTE system and to achieve higher throughput than the LTE system. According to the carrier aggregation technology, an LTE carrier (also referred to as a “component carrier”) having a maximum bandwidth of 20 MHz, which is supported by the LTE system, is used as a basic component. Then, a plurality of component carriers are simultaneously used, thereby achieving broader bandwidth communication.
According to the carrier aggregation, a mobile station (UE: User Equipment) can communicate with a base station (eNB: evolved Node B), simultaneously using a plurality of component carriers. In the carrier aggregation, a primary component carrier (PCC) and a secondary component carrier (SCC) are used. The PCC is reliable and used to maintain connectivity with a mobile station. The SCC is additionally configured for a mobile station using the PCC.
A mobile station which supports carrier aggregation includes an RF (radio frequency) chain for each component carrier. Thus, such a mobile station includes two or more RF chains. When the mobile station only communicates using the PCC without using the SCC, the RF chain for the SCC is not used. Using the RF chain which is not used for the component carrier, a received level of an adjacent cell with a different frequency can be measured. This inter-frequency measurement is herein referred to as non-gap measurement. According to the non-gap measurement, an inter-frequency cell can be measured while maintaining communication using the PCC, which can alleviate reduction of throughput on the PCC.
However, when a state change (for example, power-on/power-off, frequency shift, and so on) occurs in the RF chain which is not used for communication, an instantaneous interruption arises in another RF chain which is used for communication. For example, upon power-on/power-off in the RF chain which is not used for communication in order to perform inter-frequency cell measurement, a noise is generated in the RF chain which is used for communication and thus data cannot be received.